Several different types of knee joints in an artificial leg have been known in the art, such as adaptor knee joint, linking clutch knee joint etc. In earlier stages, an artificial leg had only a few operating modes, e.g. free knee motion, stiff knee swing or safety knee motion mode. But none of the artificial legs can automatically change mode to enable it to operate suitably for all ground conditions.
Furthermore, an artificial leg with a conventional knee joint can not guarantee an amputee's safety when he is going downhill. Besides, the ankle portion between the foot and leg in a conventional artificial leg is fixed, thus making the amputee walk unsteadily.